The present invention refers to infrared sensor devices for motor-vehicles, of the type designed to detect the presence of an overtaking vehicle. In particular, the invention concerns a device of the type comprising infrared sensors associated with the rear view mirror on the outside of the motor-vehicle and suitable for detecting the infrared radiation emitted by an overtaking vehicle.
Devices of the type described above are illustrated, for instance, in EP-A-0 673 802 and in DE-A-296 17 413. Said devices tend to reduce the potential risks deriving from the so-called xe2x80x9cblind spotxe2x80x9d on the outside rear view mirror, warning the driver of the presence of an overtaking vehicle that is hidden by the above-mentioned blind spot on the rear view mirror and that the driver would therefore be unaware of otherwise.
The drawbacks of devices of the kind mentioned above that have been developed to date are that their operation is unreliable, since they are incapable of distinguishing clearly between the presence of an overtaking vehicle and that of other vehicles traveling in the opposite direction to the vehicle on which the device is installed. Said known devices, moreover, are at risk of false alarms due to electronic and electromagnetic noise in the environment in which the vehicle moves.
With a view to overcoming said drawbacks, the object of the present invention is a sensor device of the type indicated at the beginning of the present description, characterized by the fact that it includes at least two cells that are sensitive to infrared radiation, placed on one side of the reflecting plate of the outside rear view mirror, behind focusing optics, in which each cell emits a signal that is proportional to the infrared radiation it receives, said device including an electronic circuit that emits a global signal proportional to the difference between the signals produced by the two cells, so that said global signal enables a distinction to be made between the presence of an overtaking vehicle and that of other vehicles travelling in the opposite direction, as well as reducing the likelihood of false alarms due to electronic and electromagnetic noise.
Preferably, the above-mentioned cells are pyroelectric sensors that emit a signal proportional to their temperature. Sensors of this type are marketed, for instance, by Heiman, Murata, Nippon Ceramic, etc.
Further advantages and characteristics of the invention will emerge from the description that follows, with reference to the attached drawings, provided merely by way of example and in no way restricting the scope of the invention, in which: